This invention concerns a scattered light smoke detector with an optical measuring chamber, having a sensor arrangement with at least one light source and one light receiver, and a labyrinth system with screens arranged on the periphery of the measuring chamber, the at least one light source and the light receiver each being arranged in a housing.
In the case of scattered light smoke detectors, which if required can contain, as well as the optical measuring chamber, a further sensor, for instance a temperature sensor, it is known that the optical measuring chamber is in such a form that interfering external light cannot penetrate it, and smoke can penetrate it very easily. The at least one light source and one light receiver are arranged so that no light beams can reach from the at least one light source to the receiver directly. If smoke particles are present in the path of the beam, the light from the at least one light source is scattered on them, and part of this scattered light falls on the light receiver and causes an electrical signal.
It is obvious that the reliability and security against false alarms of such scattered light smoke detectors depend essentially on their constant sensitivity. As well as the ageing of the opto-electronic components, it is in particular pollution of the light-penetrated optical surfaces of the stated components which have a negative effect on sensitivity.